I recommend you try to find some drawings or somehow learn the internal workings of the 1873.
The "lockup",if you want to call it that,is simply the toggle links that move the bolt.It is not a strong system,I am not an expert on them but I believe you will find the 1873 will not hold up well to hot rodding.
It was designed for black powder pressures;OK,the modern one with modern steels will be SAAMI safe with SAAMI .357 loads.
If it was mine,and I wanted it to last a long time.I might load 38 spl +P loads in 357 cases and make the bean cans bounce.
Again,I do not own one,and I'm not the expert,but that is my suggestion.